Conventionally, apparatuses which obtain radiographic images of objects by irradiating the objects with X-rays and detecting the intensity distributions of X-rays transmitted through the objects have been widely and generally used in the fields of industrial non-destructive testing and medical diagnosis. As a general method for such imaging, a film/screen method using X-rays is available. This method images an object by using a combination of a photosensitive film and a phosphor having sensitivity to X-rays. Rare-earth phosphor sheets which emit light upon application of X-rays are held in tight contact with the two surfaces of a photosensitive film. The phosphor converts X-rays transmitted through an object into visible light. The photosensitive film then captures the light. The method then develops, by chemical process, the latent image formed on the film, thereby visualizing the image.
The recent advances in digital technology have popularized the scheme of obtaining high-quality radiographic images by converting the intensity distribution of X-rays transmitted through an object into an electrical signal, detecting it, processing it, and then reproducing the resultant information as a visible image on a monitor or the like. As such a method of converting a radiographic image into an electrical signal, there has been a proposed radiographic image recording/reproduction system which temporarily stores X-rays transmitted through an object as a latent image in a phosphor, photoelectrically reads out the latent image by irradiating the phosphor with excitation light such as a laser beam, and then outputs the readout image as a visible image.
In addition, with the recent advances in semiconductor process technology, there has been developed an apparatus for capturing a radiographic image in the same manner as described above by using a semiconductor sensor. These systems have very wide dynamic ranges as compared with conventional radiographic systems using photosensitive films, and can obtain radiographic images which are robust against the influences of variations in the X-ray dose upon exposure. At the same times, unlike the conventional photosensitive film scheme, this method need not to perform any chemical process and can instantly obtain an output image.
Recently, a portable radiographic apparatus has also been developed, which is used when it is necessary to perform imaging in an arbitrary imaging posture. This portable radiographic apparatus may directly receive the load of an object as a static load or may possibly receive a shock load when the apparatus is dropped during transportation. As described above, the portable radiographic apparatus is required to have certain strength, enough to stand the load acting on the apparatus while protecting the internal X-ray detection unit of the apparatus.
Recently, a portable imaging apparatus like that disclosed in Japanese Patent No. 3848288 has been proposed. The X-ray detection sensor is supported on a base having high levels of strength. This base is fixed to an exterior on the lower side. The lower surface of the base has a plurality of concave portions, to which a plate member made of a carbon material is bonded to secure the strength of the sensor.
In addition, Japanese Patent Laid-Open No. 2006-311575 has proposed an apparatus which has a gas-filled vessel placed between the X-ray detection sensor and the housing to protect the sensor.
In general, improving the strength of an apparatus itself while protecting the interior of the apparatus will increase the weight and size of the apparatus itself. A portable radiographic apparatus is sometimes inserted between an operating table or the like and an object to image it on a table in an X-ray room, on a bed in a hospital ward, or on an operating table in an operating room. For this reason, the radiographic apparatus is required to be as thinner as possible to reduce the discomfort experienced by patients. When inserting the radiographic apparatus between the operating table or the like and the object at the time of imaging, an X-ray technician who operates the radiographic apparatus needs to hold the apparatus with one hand. When using a radiographic apparatus on a nursing cart on a side of a bed in a hospital ward, in particular, the technician needs to set the radiographic apparatus while holding the posture of a patient by himself/herself. The apparatus is therefore required to be smaller and lighter for a reduction in load on the technician as well.
As described above, in the case of the conventional radiographic apparatus, to improve the strength of the apparatus itself in consideration of the protection of the apparatus, it is necessary to increase the weight and size of the apparatus itself. On the other hand, in consideration of reduction in the discomfort experienced by a patient, it is required to reduce the thickness of the apparatus, whereas in consideration of reduction in the load on an operator, it is required to reduce the weight of the apparatus. That is, the conventional radiographic apparatus has such contradictory challenges.
In the apparatus disclosed in Japanese Patent No. 3848288, the support structure of the X-ray detection sensor is fastened to the exterior housing with screws to restrict the movement of the X-ray detection sensor inside the apparatus. Consider this apparatus in the thickness direction. In this case, in consideration of the head of each screw, the thickness of the housing, and a sufficient engaging amount of each screw, the apparatus needs to have a certain thickness on the rear side of the X-ray detection sensor, leading to a limitation in reduction in thickness.
The apparatus disclosed in Japanese Patent Laid-Open No. 2006-311575 is characterized in that even when the housing deforms upon application of an external shock or the like, the X-ray detection sensor inside is protected, and the housing has stability. In order to protect the X-ray detection sensor in the housing while permitting the deformation of the housing, a sufficient space must be secured between the housing and the X-ray detection sensor. This leads to a limitation in terms of reduction in the thickness.